1. Field of the Invention
The present invention relates to a field sequential color (FSC) mode liquid crystal display (LCD), and more particularly, to an FSC mode LCD in which a burst mode PWM dimming is applied to a field sequential driving scheme, thereby providing an improved luminance efficiency, a reduced color distortion, and high color reproduction and resolution, and reducing power consumption.
2. Description of the Related Art
As a cathode ray tube (CRT) become larger for a large display region, it becomes bulky and heavy. Thus, the CRT occupies a large insulation area and is difficult to carry. Due to these drawbacks, the CRT is not suitable for wall-mount TVs, whose demand is expected to increase rapidly, or monitors of portable computers.
Meanwhile, slim and light flat panel displays have been developed in order to replace the CRT. Examples of the flat panel displays include a liquid crystal display (LCD) and a plasma display panel (PDP).
Generally, the LCD includes an LCD back panel and a backlight unit. A cold cathode fluorescent lamp (CCFL) is widely used as a lamp of the backlight unit. The backlight unit is getting small-sized, slim, and lightweight. To meet this trend, light emitting diode (LED) has been proposed. The LED is advantageous over the CRT in terms of power consumption, weight, and luminance.
The LED backlight unit includes a white LED and a light guide plate for guiding light generated from the white LED. Also, the LCD back panel includes a plurality of liquid crystal cells arranged in a matrix form, a plurality of control switches (e.g., R, G and B switching transistors) for switching video signals to be applied to the liquid crystal cells, and R, G and B color filters formed on the liquid crystal cells. At this point, brightness (luminance) is adjusted using base signals of the R, G and B switching transistors, and color is adjusted using a combination of drain signals of the R, G and B switching transistors. Specifically, alignment direction of the liquid crystal cells is adjusted by the base signals and transmittance of light generated from the LED backlight unit is adjusted so that the brightness (luminance) is adjusted.
FIG. 1 is a block diagram of a conventional burst mode LCD.
Referring to FIG. 1, the conventional burst mode LCD includes a white LED backlight unit driver 10 and a white LED backlight unit 20.
The white LED backlight unit driver 10 includes a controller 11, a DC/DC converter 12, a burst mode dimmer 13, and a current source 14. The controller 11 controls a driving of the backlight unit in response to an external adjustment, and the DC/DC converter 12 converts a battery voltage (e.g., 2.8 V) into a driving voltage (e.g., 8 V) under control of the controller 11. The burst mode dimmer 13 generates a pulse width modulation (PWM) signal Spwm for adjusting the brightness according to an internal sawtooth voltage Vsaw and the dimming voltage Vdim. The current source 14 generates the driving current under control of the controller 11. A current flow of the current source 14 is turned on/off by the PWM signal outputted from the burst mode dimmer 13.
The white LED backlight unit 20 includes an LED array with a plurality of white LEDs.
FIG. 2 is a waveform diagram of main signals of the burst mode dimmer illustrated in FIG. 1.
Referring to FIG. 2, the sawtooth voltage Vsaw is compared with the dimming voltage Vdim. During a period in which the dimming voltage Vdim is lower than the sawtooth voltage Vsaw, the PWM signal Spwm maintains a high level. On the other hand, during a period in which the dimming voltage Vdim is higher than the sawtooth voltage Vsaw, the PWM signal Spwm maintains a low level.
By adjusting the dimming voltage Vdim, the duty of the PWM signal Spwm can be adjusted. By adjusting the duty ratio of the PWM signal Spwm, the turn-on time of a current flowing through the white LED backlight unit 20 can be adjusted. Consequently, the luminous intensity of the white LED backlight unit 20 can be adjusted.
The conventional burst mode LCD has a problem in that a field sequential driving is impossible because the LCD is implemented for a white LED driving scheme.
In addition, because the conventional burst mode LCD must use R, G and B color filters, its structure is complex and its resolution is lowered. Furthermore, because the conventional burst mode LCD uses the white LEDs, its color reproduction is degraded compared with the LCD using the color LED.
Moreover, the conventional LCD has a problem that causes luminance reduction and color distortion due to the color filters.